LONDON (Reuters) - One in 12 young people, mostly girls, engage in self-harming such as cutting, burning or taking life-threatening risks and around 10 percent of these continue to deliberately harm themselves into young adulthood, a study found on Thursday.

Since self-harming is one of the strongest predictors of who will go on to commit suicide, the psychiatrists who conducted the study said they hoped its findings would help galvanize support for more active and earlier intervention for people at risk.

"The numbers we're talking about here are huge," said Dr. Keith Hawton of the Centre for Suicide Research at Britain's Oxford University, who reviewed the findings at a briefing in London.

Dr. George Patton, who led the study at the Centre for Adolescent Health at the Murdoch Children's Research Institute in Melbourne, Australia, said the findings revealed a "window of vulnerability" when young people were in their mid-teens and often struggling with emotional control.

"Self-harming represents a way of dealing with those emotions," he told the briefing.

In a report of their work in the Lancet medical journal, Patton's team also said young people who self-harm often have mental health problems that might not resolve without treatment.

"Because of the association between self-harm and suicide...the treatment of common mental disorders during adolescence could constitute an important...component of suicide prevention in young adults," they said.

Self-harm is a global health problem and is especially common among girls and women aged 15 to 24. Experts say they fear rates of self-abuse in this age group may be rising.

According to the World Health Organization, almost a million people die from suicide each year, giving a mortality rate of 16 per 100,000, or one death every 40 seconds. In the last 45 years, suicide rates have increased by 60 percent worldwide.

"MELTING POT"

In this study, Patton and Dr. Paul Moran of King's College London's Institute of Psychiatry followed a sample of young people in Victoria, Australia, aged from around 15 to around 29 between 1992 and 2008.

A total of 1,802 people responded in the adolescent phase, and 149, or eight percent, of them reported self-harm. More girls than boys said they self-harmed -- with rates of 10 percent and six percent respectively, translating to a 60 percent increased risk of self-harm in girls compared with boys.

Moran said a combination of hormonal changes during puberty, brain changes in the mid-teens with the final development of the pre-frontal cortex -- the brain area associated with planning, personality expression and moderating behavior -- and environmental factors such as peer pressure, emotional difficulties and family tensions appeared to be key factors.

"Hormonal changes are highly likely to be important in creating a sort of chemical melting pot which is very ripe for environmental factors to start working on -- particularly difficult family dynamics," he said.

Cutting and burning was the most common form of self-harm for adolescents, with other methods such as poisoning, taking overdoses, and battery also featuring.

By the time the participants reached young adulthood, however, rates of self-harm dropped dramatically so that by age 29, less than one percent of participants reported deliberately doing something they knew would hurt or endanger themselves.

The researchers said while it was reassuring that around 90 percent of teenagers who report self-harm are no longer doing it in adulthood, it was also important to recognize the high risks for the 10 percent who continue to do so as they grow up.

Hawton said previous studies had shown that self-harmers who come into hospital during their teenage and young adult years are 100 times more likely than the general population to commit suicide.